Tm optical switch based on slab photonic crystals with high degree of polarization and large extinction ratio

ABSTRACT

The present invention discloses a TMOS based on slab PhCs with a high DOP and a large EXR, which comprises an upper slab PhC and a lower slab PhC; the upper slab PhC is called as a first square-lattice slab PhC with a TE bandgap, the unit cell of the first square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar includes a high-refractive-index dielectric pipe and a low-refractive-index dielectric, or a high-refractive-index flat film, or a low-refractive-index dielectric; the lower slab PhC is a second square-lattice slab PhC with a complete bandgap, wherein the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, and a normalized operating frequency of the TMOS with high DOP and large extinction ratio is 0.252 to 0.267.

This application claims priority to Chinese Application No. 201410756881.X filed on Dec. 10, 2014 and International Application No. PCT/CN2015/097051 filed on Dec. 10, 2015 and published in Chinese as International Publication No. WO/2016/091192 on Jun. 16, 2016, the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a TM optical switch (TMOS) with a high degree of polarization (DOP) and a large extinction ratio (EXR), and particularly to a TMOS based on absolute photonic bandgaps (PBGs) slab photonic crystals (PhCs) with a high DOP and a large EXR.

BACKGROUND OF THE INVENTION

In recent years, with the advent of information age, the speed and amount of information required for communication technology increase dramatically. Optical communication technologies add wings to the information age, but the information processing of nodes and routes still need electronic circuits at present, which restricts the development of communication technologies in terms of speed, capacity and power consumption. Adopting photonic integrated circuits to replace or partially replace electronic integrated circuits for communication routes certainly will become the future direction of development.

A PhC is a structure material in which dielectric materials are arranged periodically in space, and is usually an artificial crystal consisting of two or more materials having different dielectric constants.

The electromagnetic modes in an absolute PBG cannot exist completely, so as an electronic energy band is overlapped with the absolute PBG of PhCs, spontaneous radiation is suppressed. The PhC having the absolute PBG can control spontaneous radiation, thereby changing the interaction between the fields and materials and further improving the performance of optical devices.

Tunable PBGs can be applied to information communication, display and storage. For modulating at high speeds by using external driving sources, many solutions have been proposed, e.g., controlling magnetic permeability by using a ferromagnetic material, and changing dielectric constant by using a ferroelectric material.

Most of the existing optical switches are realized by using a nonlinear effect, which requires the use of high-power light for control, thus it will inevitably consume a large amount of energy. In the presence of large-scale integrated system and a large number of communication users, the consumption of energy will become enormous. At the same time, the DOP will affect signal-to-noise ratio and transmission speed.

SUMMARY OF THE INVENTION

The present invention is aimed at overcoming the defects of the prior art and providing a TMOS facilitating integration and having slab PhCs with a high DOP and a large EXR.

The technical solution adopted by the invention to solve the technical problem is as follows:

A TMOS based on slab PhCs with a high DOP and a large EXR in the present invention, comprising an upper slab PhC and a lower slab PhC connected as a whole; the upper slab PhC is a first square-lattice slab PhC with a TE bandgap, the cell of the first slab square-lattice slab PhCs includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar is arranged horizontally, the first flat dielectric pillar enables an overall upper slab PhC to form as a whole, and the first flat dielectric pillar includes a high-refractive-index dielectric pipe and a low-refractive-index dielectric in the pipe, or a high-refractive-index flat film, or a low-refractive-index dielectric; the lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, the second flat dielectric pillar is arranged horizontally, the second flat dielectric pillar enables an overall lower slab PhC to form as a whole, and the second flat dielectric pillar is a high-refractive-index dielectric pillar; the background dielectric is a low-refractive-index dielectric; and a normalized operating frequency of the TMOS with a high DOP and a large EXR is 0.252 to 0.267.

The side lengths of the high-refractive-index rotating-square pillars of the first and second square-lattice slab PhCs are respectively 0.545a to 0.554a, where a is the lattice constant of the PhC, and their rotating angles are 16.01° to 35.04° and 55° to 66.83° ; and the widths of the first and second flat dielectric pillars of the first and second square-lattice slab PhCs are respectively 0.075a to 0.082a.

The first and second flat dielectric pillars of the first and second square-lattice slab PhCs are respectively spaced 0.2a from the same side of a centers of the rotating-square pillars.

The thickness of the pipe wall in the first flat dielectric pillar in the unit cell of the first square-lattice slab PhC is 0-0.004a; and a width of the low-refractive-index dielectric in the pipe is the difference between the width of the first flat dielectric pillar and a thickness of the pipe.

The TMOS has one state that said first square-lattice slab PhC is located in an optical channel (OCH) and the second square-lattice slab PhC is located outside the OCH, and another state that the second square-lattice slab PhC is located in the OCH and the first square-lattice slab PhC is located outside the OCH.

The second square-lattice slab PhC is located outside the OCH is the optically connected state; the first square-lattice slab PhC is located outside the OCH is another optically disconnected state.

The high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than 2.

The low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5.

The normalized operating frequency of the TMOS is 0.252 to 0.267, a TM polarization EXR is −19 dB to −22 dB, the highest DOP reaches 96.5%, a TE wave within the operating band is prevented, and an isolation degree (ISD) is −20 dB to −36 dB.

Positions of the first and second square-lattice slab PhC in the OCH are adjusted by external forces, including mechanical, electrical and magnetic forces.

Compared with the prior art, the present invention has the following positive effects.

1. The optical switch is an indispensable component in an integrated optical circuit is very important for high-speed operation of a network, and large bandwidth, low energy loss, high DOP and high EXR are important parameters for evaluating switches.

2. The functions of the optical switch are realized by adjusting the positions of the first square-lattice slab PhC (the upper slab PhC) and the second square-lattice slab PhC (the lower slab PhC) in the OCH.

3. The structure of the present invention enables a TMOS with a high DOP and a large EXR.

4. The TMOS with a high DOP and a large EXR based on slab PhCs facilitates integration.

These and other objects and advantages of the present invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a structural schematic diagram of the unit cell of an upper slab PhC of the TMOS based on slab PhCs with a high DOP and a large EXR of the present invention.

FIG. 1(b) is a structural schematic diagram of a unit cell of a lower slab PhC of the TMOS based on slab PhCs with a high DOP and a large EXR of the present invention.

FIG. 2 (a) is a structural schematic diagram of a first implementation of the TMOS with a high DOP and a large EXR based on slab PhCs as shown in FIGS. 1 (a) and (b).

FIG. 2 (b) is a structural schematic diagram of a second implementation of the TMOS with a high DOP and a large EXR based on slab PhCs as shown in FIGS. 1 (a) and (b).

FIG. 2 (c) is a structural schematic diagram of a third implementation of the TMOS with a high DOP and a large EXR based on slab PhCs as shown in FIGS. 1 (a) and (b).

FIG. 3 is a photonic band map structure of the second square-lattice slab PhC shown in embodiment 1.

FIG. 4 is a photonic band map structure of the first square-lattice slab PhC shown in embodiment 1.

FIG. 5 (a) is a TE field distribution diagram in the TMOS for an normalized operating frequency (a/λ) of 0.252as shown in embodiment 2.

FIG. 5 (b) is a TM field distribution diagram in the TMOS for the normalized operating frequency of 0.252 as shown in embodiment 2.

FIG. 6 (a) is a TE field distribution diagram in the TMOS for the normalized operating frequency (a/λ) of 0.253as shown in embodiment 3.

FIG. 6 (b) is a TM field distribution diagram in the TMOS for the normalized operating frequency of 0.253as shown in embodiment 3.

FIG. 7 (a) is a TE field distribution diagram in the TMOS for the normalized operating frequency of 0.257as shown in embodiment 4.

FIG. 7 (b) is a TM field distribution diagram in the TMOS for the normalized operating frequency of 0.257 as shown in embodiment 4.

FIG. 8 (a) is a TE field distribution diagram in the TMOS for the normalized operating frequency of 0.26 as shown in embodiment 5.

FIG. 8 (b) is an optical field distribution diagram in the TMOS for the normalized operating frequency of 0.26 as shown in embodiment 5.

FIG. 9 (a) is a TE field distribution diagram in the TMOS for the normalized operating frequency of 0.267 as shown in embodiment 6.

FIG. 9 (b) is a TM field distribution diagram in the TMOS for the normalized operating frequency of 0.267 as shown in embodiment 6.

These and other objects and advantages of the present invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The terms a or an, as used herein, are defined as one or more than one, The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more.

The present invention will be further described in detail below in combination with the accompanying drawings and specific embodiments.

A TMOS with a high DOP and a large EXR based on slab PhCs in the present invention, as shown in FIG. 1(a), includes an upper slab PhC and a lower slab PhC connected as a whole; the upper slab PhC is a first square-lattice slab PhC with a TE bandgap the unit cell of the first square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar is arranged horizontally, the first flat dielectric pillar enables the overall upper slab PhC to form as a whole, and the first flat dielectric pillar includes a high-refractive-index dielectric pipe and a low-refractive-index dielectric in the pipe, or a high-refractive-index flat film, or a low-refractive-index dielectric and the low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5. As shown in FIG. 1 (b), the lower slab PhC is a second slab square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, the second dielectric is arranged horizontally, the second flat dielectric pillar enables the overall lower slab PhC to form as a whole, the second flat dielectric pillar is a high-refractive-index dielectric pillar, and the high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than 2; the background dielectric is a low-refractive-index dielectric. The normalized operating frequency (a/λ) of the TMOS with a high DOP and a large EXR is 0.252 to 0.267, and this operating band is either the TE bandgap and TM transmission band of the first square-lattice slab PhC and the complete bandgap of the second square-lattice slab PhC, or the complete bandgap of the second square-lattice PhC slab and the TE bandgap and TM transmission band of the first square-lattice slab PhC, wherein a is a lattice constant of the first and second square-lattice slab PhCs, and A is the wavelength of incident wave.

For an normalized operating frequency (a/λ) of the TMOS being0.252 to 0.267, the TM polarization EXR is −19 dB to −22 dB, the highest DOP is greater than 96.5%, the TE wave within the operating band is prevented, and the ISD is −20 dB to −36 dB; the state that the first square-lattice slab PhC is located in the OCH and the second square-lattice slab PhC is located outside the OCH is a first switch state of the TMOS with a high DOP and a large EXR, i.e., optically connected state; and the state that the second square-lattice slab PhC is located in the OCH and the first square-lattice slab PhC is located outside the OCH is a second switch state of the TMOS with a high DOP and a large EXR, i.e., optically disconnected state.

The EXR of the TMOS is a ratio of the output optical powers of the TMOS in the two states, i.e., optically connected state and optically disconnected state, and the DOP of the TMOS refers to a ratio of optical power difference to optical power sum of the TE wave and the TM wave at the output end in the switch ON state.

The first implementation of the TMOS with a high DOP and a large EXR based on slab PhCs.

The TMOS includes an upper slab PhC and a lower slab PhC connected as a whole; as shown in FIG. 2(a), rotating-square pillars in PhC are omitted in the figure, and the dashed box shows the position of a rotating-square pillar array; the upper slab PhC is a first square-lattice slab PhC with a TE bandgap, the unit cell of the first square slab lattice PhC includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar is arranged horizontally, the first flat dielectric pillar enables the overall upper slab PhC to form as a whole, the first flat dielectric pillar includes a high-refractive-index dielectric pipe and a low-refractive-index dielectric in the pipe, the thickness of the pipe wall in the first flat dielectric pillar in the unit cell of the first square-lattice slab PhC is 0 to 0.004a; and the width of the low-refractive-index dielectric in the pipe is the difference between the width of the first flat dielectric pillar and the thickness of the pipe. The lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, the second flat dielectric pillar is arranged horizontally, the second flat dielectric pillar enables the overall lower slab PhC to form as a whole, and the first flat dielectric pillar and the second flat dielectric pillar of the first and second square-lattice slab PhCs are respectively spaced 0.2a from the centers of the rotating-square pillars. The side lengths of the high-refractive-index rotating-square pillars of the first and second square-lattice slab PhCs are respectively 0.545a to 0.554a, their rotating angles are 16.01° to 35.04° and 55° to 66.83°, and the widths of the first and second flat dielectric pillars of the first and second square-lattice slab PhCs are respectively 0.075a to 0.082a; the second flat dielectric pillar is a high-refractive-index dielectric pillar, the high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than 2, and the high-refractive-index dielectric adopts a silicon material; the background dielectric is a low-refractive-index dielectric, and the low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5. The normalized operating frequency (a/λ) of the TMOS with a high DOP and a large EXR is 0.252 to 0.267, and this frequency band is either the TM transmission band and TE bandgap of the first square-lattice slab PhC and the complete bandgap of the second square-lattice slab PhC, or the TM transmission band and TE bandgap of the second square-lattice slab PhC and the complete bandgap of the first square-lattice slab PhC, wherein a is a lattice constant of the first and second square-lattice slab PhCs, and λ is the wavelength of incident wave. The TM polarization EXR is −19 dB to 22 dB, the highest DOP reaches 96.5%,the TE wave within the operating band is prevented, and the ISD is −20 dB to −36 dB.

The second implementation of the TMOS with a high DOP and a large EXR based on slab PhCs.

The TMOS includes an upper slab PhC and a lower slab PhC connected as a whole; as shown in FIG. 2 (b), rotating-square pillars in PhC are omitted in the figure, and the dashed box shows the position of a rotating-square pillar array; the upper slab PhC is a first square-lattice slab PhC with a TE bandgap, the unit cell of the first square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar is arranged horizontally, the first flat dielectric pillar enables the overall upper slab PhC to form as a whole, and the first flat dielectric pillar includes a high-refractive-index flat film; the lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, the second flat dielectric pillar is arranged horizontally, the second flat dielectric pillar enables the overall lower slab PhC to form as a whole, the first flat dielectric pillar and the second flat dielectric pillar of the first and second square-lattice slab PhCs are respectively spaced 0.2a from the centers of the rotating-square pillars, the side lengths of the high-refractive-index rotating-square pillars of the first and second square-lattice slab PhCs are respectively 0.545a to 0.554a, their rotating angles are 16.01° to 35.04° and 55° to 66.83°, and the widths of the first and second slab dielectric pillars of the first and second square-lattice slab PhCs are respectively 0.075a to 0.082a. The second flat dielectric pillar is a high-refractive-index dielectric pillar, the high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than 2, and the high-refractive-index dielectric adopts a silicon material; the background dielectric is a low-refractive-index dielectric, and the low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5. The normalized operating frequency (a/λ) of the TMOS with a high DOP and a large EXR is 0.252 to 0.267, and this frequency band is either the TM transmission band and TE band gap of the first square-lattice slab PhC and the complete bandgap of the second square-lattice slab PhC, or the TM transmission band and TE bandgap of the second square-lattice slab PhC and the complete bandgap of the first square-lattice slab PhC, wherein a is a lattice constant of the first and second square-lattice slab PhCs, and λ is the wavelength of incident wave. The TM polarization EXR is −19 dB to −22 dB, the highest DOP reaches 96.5%, the TE wave within the operating band is prevented, and the ISD is −20 dB up to −36 dB.

The three implementations of the TMOS with a high DOP and a large EXR based on slab PhCs.

The TMOS includes an upper slab PhC and a lower slab PhC connected as a whole; as shown in FIG. 2(C), rotating-square pillars in PhC are omitted in the figure, and the dashed box shows the position of a rotating-square pillar array. The upper slab PhC slab is a first square-lattice slab PhC with a TE bandgap the unit cell of the first square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, the first flat dielectric pillar includes a low-refractive-index dielectric, the background dielectric is a low-refractive-index dielectric, a slot is formed in the high-refractive-index rotating-square pillar and is filled with the low-refractive-index dielectric, and the low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5, e.g., the slot is filled with air. The lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, the second flat dielectric pillar is arranged horizontally, the second flat dielectric pillar enables the overall lower slab PhC to form as a whole, the first flat dielectric pillar and the second flat dielectric pillar of the first and second square-lattice slab PhCs are respectively spaced 0.2a from the centers of the rotating-square pillars, the side lengths of the high-refractive-index rotating-square pillars of the unit cell of the first and second square-lattice slab PhCs are respectively 0.545a to 0.554a, and their rotating angles are 16.01° to 35.04° and 55° to 66.83°; the widths of the first and second flat dielectric pillars of the first and second square-lattice slab PhCs are respectively 0.075a to 0.082a; the second flat dielectric pillar is a high-refractive-index dielectric pillar, the high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than 2, and the high-refractive-index dielectric adopts a silicon material; the background dielectric is a low-refractive-index dielectric; the normalized operating frequency (a/λ) of the TMOS with a high DOP and a large EXR is 0.252 to 0.267, and this frequency band is either the TM transmission band and TE band gap of the first square-lattice slab PhC and the complete bandgap of the second square-lattice slab PhC, or TM transmission band and TE band gap the of the second square-lattice slab PhC and the complete bandgap of the first square slab lattice PhC, wherein a is a lattice constant of the first and second square slab lattice PhCs, and X, is the wavelength of incident wave. The TM polarization EXR is −19 dB to 22 dB, the highest DOP reaches 96.5%, the TE wave within the operating band is prevented, and the ISD is −20 dB to −36 dB.

The aforesaid three implementations all take a paper surface as the reference plane, and the upper and lower slab PhCs are connected as a whole by a frame and move vertically under the action of external forces to realize the functions of the TMOS. Because the frame itself is not on the light input and output planes, i.e., the light input and output planes are parallel to the reference plane, the propagation of light is not influenced. The vertical movement of the upper and lower slab PhCs serving as a whole can be realized by micromechanical, electrical or magnetic forces. For example, a magnet may be embedded into the frame, a pressure linkage device is connected with the frame, the pressure can thus drive the black frame to move up and down, and the left and right sides of the frame are located in a groove guide rail to guarantee that the black frame moves vertically, linearly and reciprocally.

Embodiment 1

In this embodiment, different photonic band map structures in a vertical direction are obtained through the first and second square-lattice slab PhCs, FIG. 3 is a photonic band map structure of the second square-lattice slab PhC, FIG. 4 is a photonic band map structure of the first square-lattice slab PhC, and it can be known by comparison that in case that the normalized operating frequency (a/λ) range is 0.242 to 0.281, this structure enables a TMOS with a high DOP and a large EXR.

Embodiment 2

In this embodiment, the normalized photonic operating frequency (a/λ) is 0.252. By adopting the first implementation and verifying with three-dimensional structure parameters for six layers of high-refractive-index rotating dielectric pillars and six layers of high-refractive-index dielectric veins consisting of rotating pillars and connecting plates are included, the result is illustrated in FIGS. 5(a) and 5(b). It can be known from FIGS. 5(a) and 5(b) that: the TMOS has a high DOP and good extinction effect.

Embodiment 3

In this embodiment, the normalized photonic operating frequency (a/λ) is 0.253. By adopting the first implementation and verifying with three-dimensional (3D) structure parameters for six layers of high-refractive-index rotating dielectric pillars and six layers of high-refractive-index dielectric veins consisting of rotating pillars and connecting plates are included, the result is illustrated in FIGS. 6(a) and 6(b). It can be known from FIGS. 6(a) and 6(b) that: the TMOS has a high DOP and good extinction effect.

Embodiment 4

In this embodiment, the normalized photonic operating frequency (a/λ) is 0.257. By adopting the second implementation and verifying with 3D structure parameters for six layers of high-refractive-index rotating dielectric pillars and six layers of high-refractive-index dielectric veins consisting of rotating pillars and connecting plates are included, the result is illustrated in FIGS. 7(a) and 7(b). It can be known from FIGS. 7(a) and 7(b) that: the TMOS has a high DOP and good extinction effect.

Embodiment 5

In this embodiment, the normalized photonic operating frequency (a/λ) is 0.26. By adopting the second implementation and verifying with 3D structure parameters for six layers of high-refractive-index rotating dielectric pillars and six layers of high-refractive-index dielectric veins consisting of rotating pillars and connecting plates are included, the result is illustrated in FIGS. 8(a) and 8(b). It can be known from FIGS. 8(a) and 8(b) that: the TMOS has a high DOP and good extinction effect.

Embodiment 6

In this embodiment, the normalized photonic operating frequency (a/λ) is 0.267. By adopting the second implementation and verifying with 3D structure parameters for six layers of high-refractive-index rotating dielectric pillars and six layers of high-refractive-index dielectric veins consisting of rotating pillars and connecting plates are included, the result is illustrated in FIGS. 9(a) and 9(b). It can be known from FIGS. 9(a) and 9(b) that: the TMOS has a high DOP and good extinction effect.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

What is claimed is:
 1. A TMOS based on slab PhCs with a high degree of DOP and a large EXR, wherein said TMOS based on slab PhCs with a high DOP and a large EXR, comprising: an upper slab PhC and a lower slab PhC connected as a whole; said upper slab PhC is a first square-lattice slab PhC with a TE bandgap, the cell of said first slab square-lattice slab PhCs includes a high-refractive-index rotating-square pillar, a single first flat dielectric pillar and a background dielectric, said first flat dielectric pillar is arranged horizontally, said first flat dielectric pillar enables an overall upper slab PhC to form as a whole, and said first flat dielectric pillar includes a high-refractive-index dielectric pipe and a low-refractive-index dielectric in the pipe, or a high-refractive-index flat film, or a low-refractive-index dielectric; said lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of said second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, a single second flat dielectric pillar and a background dielectric, said second flat dielectric pillar is arranged horizontally, said second flat dielectric pillar enables an overall lower slab PhC to form as a whole, and said second flat dielectric pillar is a high-refractive-index dielectric pillar; said background dielectric is a low-refractive-index dielectric; and a normalized operating frequency of said TMOS with a high DOP and a large EXR is 0.252 to 0.267.
 2. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein the side lengths of the high-refractive-index rotating-square pillars of the first and second square-lattice slab PhCs are respectively 0.545a to 0.554a, where a is the lattice constant of the PhC, and their rotating angles are 16.01° to 35.04° and 55° to 66.83°; and a widths of said first and second flat dielectric pillars of said first and second square-lattice slab PhCs are respectively 0.075a to 0.082a.
 3. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein said first and second flat dielectric pillars of said first and second square-lattice slab PhCs are respectively spaced 0.2a from the same side of a centers of said rotating-square pillars.
 4. The TMOS based on absolute forbidden bands slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein the thickness of the pipe wall in said first flat dielectric pillar in the unit cell of said first square-lattice slab PhC is 0-0.004a; and a width of said low-refractive-index dielectric in the pipe is the difference between the width of said first flat dielectric pillar and a thickness of the pipe.
 5. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein said TMOS has one state that said first square-lattice slab PhC is located in an optical channel and said second square-lattice slab PhC is located outside the optical channel, and another state that said second square-lattice slab PhC is located in the optical channel and said first square-lattice slab PhC is located outside the optical channel.
 6. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 5 wherein said second square-lattice slab PhC is located outside the optical channel is the optically connected state; said first square-lattice slab PhC is located outside the OCH is another optically disconnected state.
 7. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein said high-refractive-index dielectric is silicon, gallium arsenide, titanium dioxide or a different dielectric having a refractive index of more than
 2. 8. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein said low-refractive-index dielectric is vacuum, air, cryolite, silica, organic foam, olive oil or a different dielectric having a refractive index of less than 1.5.
 9. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein said normalized operating frequency of said TMOS is 0.252 to 0.267, a TM polarization EXR is −19 dB to −22 dB, the highest DOP reaches 96.5%, a TE wave within the operating band is prevented, and an isolation degree is −20 dB to −36 dB.
 10. The TMOS based on slab PhCs with a high DOP and a large EXR, as claimed in claim 1 wherein positions of said first and second square-lattice slab PhC in the OCH are adjusted by external forces, including mechanical, electrical and magnetic forces. 